@ikkeT what cap did you put on the nrf?
because i also did have problems with transmission and i solved it with other caps in parrallel on vcc and gnd!
when on batteries:
10uf elektrolitic
0.1nf ceramic
100uf tantalum
on the voltage regulator i think also before 0.1nf and a 10uf to lower the noise on the power line output
what you think about that?
grtz